Democratic leaders said Mr. Burris, a Democrat appointed by Illinois Gov. Rod R. Blagojevich amid federal corruption charges he offered to sell that Senate seat, could be blocked from entering the chamber for the swearing-in ceremony Tuesday.

But Mr. Burris still is expected to arrive Monday in Washington and attempt to gain access to the Senate floor as Illinois’ appointed junior senator.

“As of this moment, he is not allowed on the Senate floor,” a senior Democratic aide said.

Mr. Franken, a Democrat holding a 225-vote lead in a fiercely contested recount battle with incumbent Republican Sen. Norm Coleman, will run into a Republican filibuster if he tries to take the oath.

“I can assure you that there will be no way that people on our side of the aisle will agree to seat any senator without a valid certificate,” Sen. John Cornyn of Texas, the incoming chairman of the National Republican Senatorial Committee, said Friday in a conference call with reporters.

Political turmoil is unheard of in a Senate swearing-in ceremony, and the drama threatens to mar the start of a session in which the Democrat-led Congress has high hopes for working with President-elect Barack Obama, including plans to pass a massive economic stimulus in the next three weeks.

“This is a big distraction for them,” a Republican leadership aide said. “It is not what they want to be talking about right now.”

Neither the appointment of Mr. Burris nor the election of Mr. Franken has been certified by state officials, making it difficult for them to demand to be seated.

Illinois Secretary of State Jesse White has refused to certify the appointment by Mr. Blagojevich — a step that is legally required but is almost always a pro forma move.

He said that while Mr. Burris, a former Illinois attorney general, is highly qualified and respected in the state, the charges against Mr. Blagojevich, which include trying to sell Mr. Obama’s now-vacant seat, sully the entire process of appointing a successor.

“Quite simply, the cloud of controversy surrounding the governor prohibits me from accepting a document that certifies any appointment made by Rod Blagojevich for the vacant U.S. Senate seat from Illinois,” Mr. White said in an Op-Ed column distributed to the press. “Such an appointment, regardless of the merits of the appointee, would be tainted by scandal, and our state deserves better.”

Democrats are under increasing pressure from liberal activists to accept Mr. Burris, who is black and would succeed Mr. Obama as the only black member of the Senate.

He said that even if the Burris appointment was certified, it would be referred to a Senate committee for investigation — a move intended to stall the appointment long enough for the Illinois legislature to finish impeachment proceedings against Mr. Blagojevich.

On Friday, the Illinois legislature moved up its schedule to hasten impeachment hearings.

Mr. Reid’s own objectivity has come under attack.

According to a report Friday in the Chicago Sun-Times, Mr. Reid called Mr. Blagojevich to discuss the seat Dec. 3 and talked down three possible candidates — Rep. Jesse L. Jackson Jr., Rep. Danny K. Davis and retiring state Senate President Emil Jones — and boosted two others — state Veterans Affairs Director Tammy Duckworth and state Attorney General Lisa Madigan.

The three men Mr. Reid reportedly tried to discourage are all black; neither of the two women are.

Reid spokesman Jim Manley confirmed that a conversation took place, but declined to give details and said his boss also spoke to other Democratic governors about filling vacancies in their states.

“I think the governor believes there is a conflict of interest — that Reid showed he has a horse in the race, and Roland Burris wasn’t one of them,” Blagojevich spokesman Lucio Guerrero told the Associated Press.

Black activists in Illinois also have made race claims, with about a dozen calling a Chicago news conference Friday saying that Mr. Burris is qualified and should not be punished for Mr. Blagojevich’s legal woes, with which he has no connection. And separately, Rep. Donald Payne, New Jersey Democrat, said that because Mr. Burris is qualified, the Senate “should reconsider” and because the Democrat-led Senate risks having no black members.

“There is a legitimate opportunity to have the Senate at least start to look a teeny bit like America,” he said.

Burris attorney Timothy Wright has threatened to go to court to force the Senate to seat his client if the chamber refuses to do so.

For Mr. Franken, a former “Saturday Night Live” comedian, Minnesota law prevents certification of an election until legal challenges are resolved, and the anticipated lawsuit by the loser, whoever he is, will take weeks if not months.

Minnesota’s other senator, Democrat Amy Klobuchar, called for Mr. Franken to be seated temporarily while the legal battle runs its course. Mr. Franken did not respond to inquiries Friday about his next move.

Attempting to seat Mr. Franken as a provisional senator would pose political pitfalls for Democrats. They would face criticism for applying a double standard by seating Mr. Franken, who is white, and not Mr. Burris when neither has been certified for the post by his home state.

Democrats also would have a hard time beating a Republican filibuster and risk suffering an embarrassing early defeat as Democrats prepare to assume control at both ends of Pennsylvania Avenue. Senate Democrats will have a 57-vote majority without Mr. Burris or Mr. Franken, short of the 60 votes needed to end a filibuster. Adding those two men would only bring the total to 59, still short of 60.

Mr. Cornyn urged all parties to respect Minnesota’s process.

“I think it is very clear that the people of Minnesota and the courts in Minnesota should make the decision about who won the Minnesota Senate election, and not political leaders in Washington, D.C.,” the Texan said. “That process is ongoing and will not be resolved, in all likelihood, for weeks and maybe longer.”